Exogenous and Endogenous rhythms

Enogenous is where control of biological rhythms is exerted from within.

The suprachiasmatic nucleus is the pacemaker of the biological clock, which lies in the hypothalamus. It generates its own biological rhythm and is connected to the optic chiasm, so recieves information about the amount of light, this in turn causes melatonin release. The SCN sends signals to the pineal gland, directing it to increase levels of melatonin at night.